code: def test_iht_fit_resample_default_estimator():
      iht = InstanceHardnessThreshold(
          estimator=None, random_state=RND_SEED
      )
      X_resampled, y_resampled = iht.fit_resample(X, Y)
      assert isinstance(iht.estimator_, RandomForestClassifier)
      assert X_resampled.shape == (12, 2)
      assert y_resampled.shape == (12,)
  
file_path: imbalanced-learn/imblearn/under_sampling/_prototype_selection/tests/test_instance_hardness_threshold.py
imports: import numpy
  from sklearn.ensemble import GradientBoostingClassifier, RandomForestClassifier
  from sklearn.naive_bayes import GaussianNB
  from sklearn.utils._testing import assert_array_equal
  from imblearn.under_sampling import InstanceHardnessThreshold
label_desc: Use image node_id 6 for calling a global function with example usage: test_iht_fit_resample_default_estimator() without return types